Welcome to V Flyer.
My hubby and I went to NY for the first time in November just gone, we had a fabulous time.
Have a look here at my trip report for the outward flight.
forum/index.php?f=6&t=283734&rb_v=viewtopicWe went on G's which is a ticket all paid for by miles (80k each), in Upper Class and the taxes cost about £1k for the two of us. In my opinion it isn't the best use of miles but I wanted to use some up.
The most efficient method (sales aside) is to book (an upgradeable bucket) and upgrade with miles. I would personally not fly in Y (economy) so would only ever upgrade from a PE ticket. I'm not as knowledgeable as others on which buckets are upgradable, so I will leave that for someone else to explain. But there's plenty of time for you to max out your earning points potential between now and the end of the year (which is when you will start to see next years flights appear) depending on when you are planning to go exactly.
If you want to collect miles, then use things like your Tesco club card points to auto tip into you Flying Club (FC) account. Subscribe to this forum and Head For Points (which send out a few points earning emails every morning) and check in for sales/offers on both here and the Virgin website.
I used the Trip Advisor NYC forum for further help on NYC itself. We stayed in the Hilton Garden Inn Times Square, which was close enough to the action without being 'neonned-out' at night! We are Hilton Gold and managed a free upgrade and freebie breakfast every morning. A little scant through Flytertalk forum and we did find several discount codes. We paid a little over £500 (4 nights) for their top floor, biggest room. The view was amazing. But wherever you stay, research it, find out if you can earn an upgrade and always always contact the hotel in advance to explain it's a special anniversary. Our stay was a wedding anniversary and it did mean little extras/freebies in the hotel when we arrived…
We flew in on the Monday before Black Friday (into JFK on the Monday and home from EWR on the Friday) It was short, exciting, tiring but long enough. We managed to do all the sites, loads of shopping and it was fairly quiet and inexpensive before the big Thanks Giving weekend - actual Thanks Giving was our last night there and it did allow us to see a bit of the parade and join in the party!
Have a wonderful time and have fun organising it. Just a word of warning though, you might just get so excited you have to let her know! A surprise is great fun, but so is the anticipation of the holiday too.